Maybe they'll switch to the system of preregistering. Then you'll be able to sign both kids up for the same show.
My favorite way to start the day is with a visit to Fantasyland. If we can get on Peter Pan within the first 10 minutes, we'll go there first. Otherwise we skip it and go straight to Alice. Then we head to Dumbo and ride all of the main area Fantasyland rides generally alternating between an inside ride and an outside ride. So long as you don't waste time on Peter Pan, you can do the majority of the Fantasyland rides in the first hour. If this was an early entry day the park would be opening. This allows you to finish up Fantasyland with canal boats, Matterhorn, and Small World. We like to go to Toon Town around the time it opens (1 hour after regular park opening). There is a short ceremony where Mickey walks kids into the town. There's a fun little coaster back there that little kids enjoy. We'll typically ride this several times in a row and then maybe catch a ride on Roger Rabbit. We always make sure we stop for pictures with characters around Toon Town. If it was an early entry day, the 3 hours would be about up. If it wasn't an early entry day we would have gone to Toon Town when it opened during the second hour and would still need to ride Small World, Matterhorn, and the Canal boats. Either way you can do all of Fantasyland and Toon Town in about 3 hours.
Another option, for non early entry day, would be to head to Adventureland first. Grab a FP for Indy and jump on one of the first boats through the Jungle. You can pretty much choose what rides to do on this side of the park during the first couple of hours as most guests are in other areas of the park. You can easily ride every ride on this side of the park within the first three hours: Jungle Cruise, Indy, Pirates, Haunted Mansion, Pooh, Splash Mountain, River Cruise (it'll be closed though), Big Thunder. It's a really good place to head if you want to avoid the crowds in the morning.